The operating principle of neutron detectors is based on the interaction of neutrons, for example thermal (energy of 0.025 eV i.e. in thermal equilibrium in a medium at 20° C.), with atoms and/or nuclei of a neutron-converting material. For example the interaction of neutrons with the Boron-10 isotope (10B) produces alpha (4He) and lithium (7Li) particles (nucleus). According to a configuration example the particles are generated in opposite directions according to the following reactions (and their associated probabilities) with an energy Q:10B+neutron→7Li+4He (Q=2.72 MeV) 6%10B+neutron→7Li+4He (Q=2.31 MeV) 94%
The detector as such requires the presence of a Neutron Conversion Layer (NCL) in order to convert in fine the incident neutrons into electron-hole pairs.
The ionization of the material, produced by the generation of 7Li and 4He particles/nuclei, can then be detected thanks to the electric field present at the terminals of a Space Charge Region (SCR). The space charge region (SCR), also called depletion zone, or deserted zone, corresponds to the region that appears in a p-n junction, between an n-doped region and a p-doped region. It is called “depletion zone” or “deserted zone” because it is devoid of free carriers, and it is called “space charge region” because it is comprised of two electrically charged regions (contrary to the rest of the semiconductor n and of the semiconductor p which are globally neutral). As such, a detector requires the presence of a p-n junction in order to generate said space charge region and as such collect the carriers coming from the aforementioned reactions.
The document “Nuclear Radiation Detector Based on Ion Implanted p-n Junction in 44-SiC”, relates to a detector of thermal neutrons. This detector comprises a thick layer of the n+ type formed by SiC, a p+ doped layer by implantation of aluminum (Al+) ions in the n+ layer of SiC. The p+ doped layer defines with the n+ doped layer the space charge region (SCR) which extends in the n+ layer from the n/p interface. Moreover, the detector comprises a layer that is rich in the boron-10 isotope (10B) forming the neutron conversion layer (NCL). Furthermore, this neutron detector requires polarization. This document discloses that an increase in the polarization makes it possible to improve the quality of the signal.
This detector is globally satisfactory. On the other hand, it has been shown that it delivers results that are unstable over time.
This invention aims to propose a solution to overcome this disadvantage.